1. Field of the Invention
The present invention relates generally to lap grinding and polishing of substrates including optics and, more particularly, to a system utilizing ultrasonic energy to enhance the rate of removal of micron-thicknesses of material from a substrate. Throughout this disclosure, the terms "lap" and "lapping" and their derivatives will be used to refer to a process of producing an extremely accurate, highly finished, surface by means of a block charged with abrasive. The block, or lap, may be a pitch-covered metal tool or a metal tool covered with pitch-impregnated felt. Lapping is intended to encompass sequential operations of grinding and polishing. The amount of material typically removed by lapping does not exceed approximately 0.0002 inches to 0.0005 inches.
2. Description of the Prior Art
Conventional grinding and polishing operations rely primarily on two mechanisms: mechanical and chemical. The mechanical removal mechanism consists of a shear of the surface atoms when the lap provides a high local pressure at the contact points between the abrasive and the optic surface. This is aided by a chemical removal mechanism, which for most cases, entails the formation of a soft hydrolyzed layer by reaction with water that is subsequently removed by the abrasive.
While ultrasonics abrasion is known for drilling, it has not previously been used for polishing or for use in semiconductor processing applications.